It is known that optimal viral yields are obtained by harvesting a virus when the viral titer is at a maximum. It frequently happens, however, that the maximum viral titer occurs outside of normal working hours, e.g. during weekends, on holidays, or at night. In such an event the virus can either be harvested when at its maximum titer with personal inconvenience to employees and with increased labor cost, or it can be harvested during the next regular work period with possible loss of titer.